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Junction potentials in electrochemical cells with transference: A review and prescription to end over 70 years of sleepwalking
Journal article   Open access   Peer reviewed

Junction potentials in electrochemical cells with transference: A review and prescription to end over 70 years of sleepwalking

Peter M. May and Eric F. May
Electrochimica acta, Vol.539, 147087
2025
DOI: https://doi.org/10.1016/j.electacta.2025.147087
Appears in  Open Access via Read & Publish Agreements
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CC BY V4.0,  Open Access

Abstract

Individual ion activity coefficients Liquid junction potentials Salt bridges Single ion activity coefficients Thermodynamic axioms Thermodynamic conventions
Modern improvements in potentiometric technology (apparatus and digitisation) have overcome many persistent electrochemical issues yet important fundamental problems remain unsolved. Junction potentials in cells with transference have, in particular, long been a scientific enigma with serious practical consequences. This review highlights the fundamental role played by junction potentials, which have wide-ranging implications for the measurement of pH in electrolyte solutions of practical interest. Ending the sleepwalking around junction potentials is an essential step in a prospective redefinition of pH. We emphasise here that, relative to a reference electrode shielded by an electrolytic bridge, a junction potential profile often can be determined experimentally; this can be done without thermodynamic ambiguity as a function of electrolyte concentration. Coupled with a practical convention for single ion activity coefficients, measurements using an appropriate electrode sensor in the sample can accurately quantify changes in the junction potential from high to low ionic strengths. These data can then be supplemented by further measurements with well characterised pH buffers, so as to extrapolate the junction potential profile to infinite dilution. In this way pH can be better defined and measured, enabling its present range to be greatly extended. For many scientific applications that require more than just precise comparisons of acidity, improved pH accuracy can be expected. In particular, routine analyses of multicomponent aqueous solutions using glass electrode potentiometry should be greatly enhanced. Legend: Current pH ailments can be cured by the ubiquitous combination glass electrode if junction potential uncertainties can be resolved. [Display omitted]

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